1. Field of the Invention
The present invention relates to a copying machine of a type equipped with a recirculating document handling mechanism for automatically feeding a plurality of sheet-like documents to be copied onto a document reading station one at a time. The present invention is particularly suited for, although not exclusively limited to, use with sheet-like documents each having an image on both sides thereof.
In the description to follow, the following terms used herein for the purpose of the present invention are to be construed having the following respective meanings.
"Duplex document": a sheet-like document which has its opposite sides bearing respective images to be copied. PA1 "Duplex copy": a copying or recording sheet having its opposite sides copied with respective images. PA1 "Simplex document"; a document which has only one side bearing an image to be copied. PA1 "Simplex copy": a copying or recording sheet having only one side copied with an image.
2. Description of the Prior Art
Most of the conventional electrophotographic copying machines of the slit exposure type in which a document to be copied is scanned by an optical system are equipped with a recirculating document handling mechanism (RDH) designed to feed a plurality of sheet-like documents to be copied automatically one at a time onto a document reading station so that each document can be read by an optical reader held at a predetermined position.
FIG. 1 illustrates, in schematic side sectional representation, an electrophotographic copying machine 1 equipped with a recirculating document handling mechanism that is employed in the practice of the prior art as well as the present invention. The electrophotographic copying machine 1 comprises a machine housing 2 having the recirculating document handling mechanism 3 and a document presser plate 4 both mounted atop the machine housing 2.
In order to make duplex copies from duplex documents with page layouts of each duplex copy identical with those of the corresponding duplex document, it is a general practice to place a stack of duplex documents within a document tray 5. Each of the stacked documents within the document tray 5 is transported by means of a feed roller 6 towards a first reading station 7 at which the respective document can be illuminated by an illuminator lamp 10 so that information on one of the sides of such a document can be read. After information on the respective side of the document has been read out at the first reading station 7, such document is turned upside down by a document inverting means 8 and is then transported to a second reading station 9 at, which information on the other remaining side of the document can be read out. At the second reading station 9, this other side of the document is illuminated by the illuminator lamp 10.
Imagewise rays of light reflected from the document at any one of the first and second reading stations 7 and 9 can be transmitted towards a photoreceptor drum 12 through an optical system 11 and is then projected onto a photosensitive surface of the photoreceptor drum 12 at exposure station 13. Since at this time the photosensitive surface of the photoreceptor drum 12 has been electrostatically charged by a primary corona discharger 14, projection of the imagewise rays of light onto the photosensitive surface of the photoreceptor drum 12 at the exposure station 13 results in a formation of an electrostatic latent image on the photosensitive surface in complemental relationship with an image on each side of the document. The electrostatic latent image so formed is then developed by a developing unit 15 into a visible toner image which is subsequently transferred at a transfer station by the action of a transfer corona discharger 18 onto a copying sheet that has been supplied from a sheet supply cassette 16 by means of a sheet feed roller 17.
The copying sheet bearing the visible toner image which has been transferred from the photosensitive surface of the photoreceptor drum 12 is then supplied through a fixing unit 19 by which the visible toner image can be permanently fixed to one side of the copying sheet. In order to make a copy on the other side of the copying sheet thereby to complete a duplexed copy, the copying sheet having one of the sides copied with an image from one of the sides of the duplexed document, is supplied towards an intermediate tray 21 through a sheet inverting means 20. Thereafter, the copying sheet once supplied to the intermediate tray 21 is drawn by a sheet feed roller 22 out of the intermediate tray 21 and towards the photoreceptor drum 12 for receiving a similarly visible toner image, corresponding to an image on the remaining side of the duplex document, from the photoreceptor drum 12 at the transfer station on the other or remaining side of the copying sheet. After the visible toner image has been transferred onto this other side of the copying sheet, the latter is transported through the fixing unit 19 so that the visible toner image can be permanently fixed thereto and is then ejected onto a copy receiving tray 23, thereby completing the duplex copying.
FIG. 6 comprised of FIGS. 6(a) to 6(h) illustrates the sequence of making the duplex copies from a plurality of simplex documents, for example, the first and second simplex documents Da and Db. It is to be noted that, in the following description, reference character "D" used to denote a document to be copied and to which a lower case "a" is affixed is intended to mean a first document while the same reference character "D" to which a lower case "b" is affixed is intended to mean a second document to be copied subsequent to the copying of the first document and that numerals "1" to "4" affixed to any one of reference characters "Da" and "Db" are intended to represent a page number of the first or second document. For example, the first page of the first document is designated by "Dal" and the third page of the second document is designated by "Db3". It is also to be noted that each copying sheet generally identified by P is shown to have its opposite sides designated respectively by Pa and Pb in correspondence with the first and second document Da and Db, respectively, and reference characters "Pa" and "Pb" are affixed with one of the numerals "1" to "4" to denote the page number of each of the documents.
In addition, for the purpose of quick reference, throughout the accompanying drawings, particularly FIGS. 6 and 7 as well as FIG. 4, each document Da or Db is shown as affixed on its opposite sides with numerals ("1" to "4") each representing the page number, while each odd-numbered page is indicated by a blank triangle. Also, so far as each copying sheet P is concerned, any one of the opposite sides of the copying sheet P which has been copied with an image is shown as having a numeral representative of the page number of the document on which such image has been born while each odd-numbered page is indicated by a blackened triangle. It is, however, to be noted that no affix will be employed to any one of the reference characters "D" and "P" used to denote the document and the copying sheet where the document or the copying sheet is collectively referred to in the description.
In order to make a duplex copy from each of the simplex documents, as shown in FIG. 6(a), the documents D to be successively copied are placed on the document tray 5 in a stacked form and in the sequentially paginated order with the initial page placed atop the stack of documents. A batch of copying sheets P is accommodated within the sheet supply cassette 16 in a stacked form.
When duplex copying is initiated, as shown in FIG. 6(b), the first document Da placed on the top of the stack of documents D within the document tray 5 is transported to the first reading station 7 at which the first page Da1 of the first document Da is scanned so that an image on the first page Da1 can be copied in any known manner on one side Pal of the first copying sheet Pa. Then, as shown in FIG. 6(c), the first document Da having its first page Da1 scanned at the first reading station 7 is subsequently transported to the document inverting means 8 and, on the other hand, the second document Db is transported to the first reading station 7 so that a copy can be made on one side Pb3 of the second copying sheet Pb.
As shown in FIG. 6(d), each of the first and second documents Da and Db whose first sides have been successively scanned at the first reading station 7 are transported past the second reading station 9 without being scanned through the document inverting means 8 and are returned to the document tray 5. On the other hand, the first and second copying sheets Pa and Pb, having one side on which a copy has been made, are successively transported through the sheet inverting means 20 onto the intermediate tray 21 and stacked therein. In this way, an image on one of the sides of each of the first and second documents Da and Db has been copied on one side of the associated copying sheet Pa or Pb.
In order to make a copy of an image on the other or opposite side of each of the, first and second documents Da and Db on the other or opposite side of the associated copying sheet Pa or Pb, the first and second documents Da and Db are successively transported again onto a reading station. As shown in FIG. 6(e), the first document Da drawn from the document tray 5 again onto the reading station is moved past the first reading station 7 without being scanned and towards the document inverting means 8. Thereafter, as shown in FIG. 6(f), at the second reading station 9, the second page Da2 of the first document Da is scanned so that an image on the second page Da2 of the first document Da can be copied on the other side Pa2 of the first copying sheet Pa which has been supplied from the lowermost position of the stack of copying sheets within the intermediate tray 21. In a manner similar to the copying on the first copying sheet Pa, as sequentially shown in FIGS. 6(g) and 6(h), the fourth page Db4 of the second document Db is scanned at the second reading station 9 so that an image of the fourth page Db4 can be copied on the respective side Pb4 of the second copying sheet Pb supplied from the intermediate tray 21. Thereafter, the first and second documents Da and Db are successively returned to the document tray 5 while the copying sheets Pa and Pb are successively ejected onto the copy receiving tray 23 after having passed through the fixing unit 19.
FIG. 7 comprised of FIGS. 7(a) to 7(h) illustrates the sequence of making the duplex copies from a plurality of duplex documents, for example, the first and second duplex documents Da and Db as is the case with the example shown in FIG. 6.
In order to make a duplex copy from each of the first and second duplex documents, as shown in FIG. 7(a), the documents D to be successively copied are placed on the document tray 5 in a stacked form and in the sequentially paginated order with the initial page placed atop the stack of documents. A batch of copying sheets P is accommodated within the sheet supply cassette 16 in a stacked form.
When duplex copying is initiated, as shown in FIG. 7(b), the first document Da placed on the top of the stack of documents D within the document tray 5 is transported to the first reading station 7 at which the first page Da1 of the first document Da is scanned so that an image on the first page Da1 can be copied in any known manner on one side Pal of the first copying sheet Pa. Then, as shown in FIG. 7(c), the first document Da having its first page Da1 scanned at the first reading station 7 is subsequently transported to and temporarily held at the document inverting means 8 while the first copying sheet P2, having the image copied on one side Pal thereof is transported through the sheet inverting means 20 to the intermediate tray 21.
Then, as shown in FIG. 7(d), the first document Da having passed through the document inverting means 8 is transported to the second reading station 9 at which the second page Da2 of the first document Da is scanned so that an image on the second page Da2 thereof can be copied on the other side Pa2 of the first copying sheet Pa which has been supplied from the intermediate tray 21. The first document Da having both its sides scanned at the first and second reading stations 7 and 9, respectively, at different timings is subsequently returned to the document tray 5 while, on the other hand, the first copying sheet P2, having both its sides copied with the images on the first and second pages Da1 and Da2 of the first document Da, is ejected through the fixing unit 19 onto the copy receiving tray 23. It is to be noted that, when the first document Da is returned to the document tray 5, the first document Da is inserted in between the bottom of the document tray 5 and the lowermost member of the stack of documents in the document tray 5.
After the first document Da has been so returned to the document tray 5, images on the remaining opposite side of the second document Db are successively copied on the respective opposite side of the second copying sheet Pb in a manner similar to the copying of the images of the first document Da on the first copying sheet P3, and as sequentially shown in FIGS. 7(e) to 7(h).
According to the first mentioned duplex copying method shown in and described with reference to FIG. 6, each document D is required to be transported twice into the passages in the recirculating document handing mechanism 3 and, therefore, there is the possibility that the document D may be damaged. Also, during a period in which the document D is circulated once from the first reading station 7 to the second reading station 9 through the document transport passage, the associated copying sheet P is required to be retained temporarily at the intermediate tray and, therefore, one cycle of the duplex copying operation tends to take a relatively long time to complete. In addition, the intermediate tray must have a size required to accommodate the plural copying sheet generally equal in number to the maximum possible number of documents to be copied and, therefore, the utilization of the limited space available within the machine housing tends to be adversely affected
On the other hand, according to the second mentioned duplex copying method shown in and described with reference to FIG. 7, each document may be once transported into the passages in the recirculating document handling mechanism 3 and, therefore, the possibility of the document being damaged can be advantageously minimized. Also, the intermediate tray may have a size sufficient to accommodate at least a single copying sheet since only one copying sheet is transported to the intermediate tray during one cycle of the duplex copying operation. Therefore, the utilization of the limited space available within the machine housing can be advantageously maximized and, hence, the length of time required to complete a copying job can be advantageously reduced.
However, after the copying of the image on one side of the document D onto one side of the copying sheet P, the copying sheet P is required to be transported through the sheet inverting means 20 to the intermediate tray and to be subsequently drawn out from the intermediate tray in readiness for the copying of an image on the remaining other side of the document onto the corresponding other side of the copying sheet. During the period in which the copying sheet is circulated past the intermediate tray, the document D is required to be temporarily held in the document inverting means and, at this time, no scanning operation can take place. Therefore, the second mentioned prior art duplex copying method has a disadvantage in that each cycle of the duplex copying operation takes a relatively long time and, therefore, the utilization of the time required to complete a copying job cannot be maximized.